Device for magnifying displacement of piezoelectric element or the like and method of producing same

ABSTRACT

A device for magnifying displacement of a piezoelectric element adapted to be displaced by application of voltage thereto, comprising a frame extending substantially parallel to a direction of displacement of the piezoelectric element; a movable member fixed to a first end of the piezoelectric element with respect to the direction of displacement; a first mount surface formed on said frame and extending substantially parallel to the direction of displacement; a second mount surface formed on the movable member and extending substantially parallel to the direction of displacement, which second mount surface is opposed to the first mount surface; a first leaf spring mounted at a first end portion on the first mount surface and extending substantially parallel to the direction of displacement; a second leaf spring mounted at a first end portion on the second mount surface and extending substantially parallel to the direction of displacement; and a rolling member fixed to second end portions of the first and second leaf springs, wherein when the piezoelectric element is displaced, the second leaf spring is displaced along the first leaf spring through the movable member to roll the rolling member.

BACKGROUND OF THE INVENTION

The present invention relates to an actuator for driving a printing wireor the like in a printing head, for example, and more particularly to adevice for magnifying displacement of a piezoelectric element or thelike as a driving source wherein expansion and contraction of thepiezoelectric element is magnified through a rolling motion of a rollingmember into a relatively large movement of the printing wire to carryout a printing operation of the printing wire. The present inventionalso relates to a method of producing such a device as mentioned above.

There are various known devices as mentioned above. For example, thereis disclosed in Japanese Patent Laid-Open Publication No. 57-187980 adevice for magnifying displacement of a piezoelectric element as shownin FIGS. 39(A) and 39(B). Referring to FIGS. 39(A) and 39(B) which showa rest condition and an operative condition of the device, respectively,a piezoelectric element 302 is fixed to a frame 300, and a rollingmember 308 is connected through a pair of leaf springs 304 and 306spaced a given distance from each other to the piezoelectric element 302and the frame 300. As shown in FIG. 39(B), when the piezoelectricelement 302 is expanded, the rolling member 308 is rolled about aconnecting portion between the same and the leaf spring 306 by themoment generated at a connecting portion of the rolling member 308 andthe leaf spring 304. Thus, the displacement of the piezoelectric element302 is converted into a rolling motion of the rolling member 308.

However, such a conventional displacement magnifying device cannotexhibit a large magnification rate of displacement of the piezoelectricelement 302 which is to be magnified and transmitted to the rollingmember 308. Accordingly, in the case of driving a printing wire, it isnecessary to lengthen the rolling member 308, so as to obtain asufficient stroke of the printing wire. Such a large size and anincreased mass of the rolling member 308 cause a problem in high-speedoperation of the printing wire.

In the case that the displacement magnifying device as shown in FIGS.39(A) and 39(B) is utilized in a printing head for a wire dot printer(not shown), for example, a printing wire is connected directly to oneend of the rolling member 308 or indirectly such as through anothermember to the one end of the rolling member 308, thus constructing aprinting unit. A plurality of a printing units of the number equal tothat of the printing wires are installed in the printing head. Eachprinting unit includes the piezoelectric element 302, and lead wiresextending from both electrodes of the piezoelectric element 302 areguided to a certain wiring board, and are connected to feeder linesformed on the wiring board by soldering or the like. However, in theconnection of the lead wires, they tend to be tangled with each other,making the connecting operation difficult. Further, .[.i.]. .Iadd.it.Iaddend.is also difficult to recognize the polarity of the lead wires.

Furthermore, the plurality of printing units are usually located betweentwo parallel base plates, and the frame 300 of each printing unit isfixed to the base plates by a suitable fixing means such as boltsdirected parallel to a direction of displacement of the piezoelectricelement 302. However, in fixing the frame 300 to the base plates, theframe 300 is expanded parallel to the direction of displacement of thepiezoelectric element 302. Further, a fixed position of the frame 300with respect to the direction parallel to the direction of displacementis slipped.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide a device formagnifying displacement of a piezoelectric element, including a pair ofleaf springs displaceable in receipt of displacement of thepiezoelectric element, which device may improve a magnification rate ofthe displacement of the piezoelectric element.

It is a second object of the present invention to provide a device formagnifying displacement of a piezoelectric element, including a pair ofleaf springs displaceable in receipt of displacement of thepiezoelectric element, which device may reduce friction between the leafsprings and thereby smoothen the displacement of one of the leaf springsrelative to the other leaf spring.

It is a third object of the present invention to provide a device formagnifying displacement of a piezoelectric element, including a pair ofleaf springs displaceable in receipt of displacement of thepiezoelectric element and a rolling member fixed to the leaf springs,which device may reduce stress at a fixed portion between the leafsprings and the rolling member and thereby improve the durability of thefixed portion.

It is a fourth object of the present invention to provide a device formagnifying displacement of a piezoelectric element, including a pair ofleaf springs displaceable in receipt of displacement of thepiezoelectric element and a rolling member fixed to the leaf springs,which device may improve the durability of a fixed portion between theleaf springs and the rolling member and reduce the number of parts.

It is a fifth object of the present invention to provide a device formagnifying displacement of a piezoelectric element, including a pair ofleaf springs displaceable in receipt of displacement of thepiezoelectric element and a movable member provided at an end of thepiezoelectric element for displacing one of the leaf springs relative tothe other leaf spring, which device may prevent inclination of themovable member due to a reaction force from the leaf spring displaced tothereby prevent a reduction in magnification rate of the displacement.

It is a sixth object of the present invention to provide a method ofproducing a device for magnifying displacement of a piezoelectricelement, including a frame, a movable member, a rolling member and apair of leaf springs assembled with the movable member and the rollingmember, which method may improve the accuracy of distance andparallelism between the movable member and a base portion of the framein installation of the piezoelectric element therebetween.

It is a seventh object of the present invention to provide a device formagnifying displacement of piezoelectric elements to be electricallyconnected through lead wires to feeder lines, which device may make easythe connection between the lead wires and the feeder lines and preventthe lead wires from being tangled.

It is an eighth object of the present invention to provide an impact dotprinting head adapted to be driven by a plurality of printing unitsincluding piezoelectric elements and frames which units are fixedlysupported between two base plates, which printing head may preventexpansion of the frame in fixing the printing units to the base platesand also prevent slippage of fixed positions of the frames.

According to a first aspect of the present invention, there is provideda device for magnifying displacement of a piezoelectric element adaptedto be displaced by application of voltage thereto, comprising a frameextending substantially parallel to a direction of displacement of thepiezoelectric element and mounting the piezoelectric element thereon, amovable member fixed to one end of the piezoelectric element withrespect to the direction of displacement, a first mount surface formedon the frame and extending substantially parallel to the direction ofdisplacement, a second mount surface formed on the movable member andextending substantially parallel to the direction of displacement, saidsecond mount surface being opposed to the first mount surface, a firstleaf spring mounted at its one end portion on the first mount surfaceand extending substantially parallel to the direction of displacement, asecond leaf spring mounted at its one end portion on the second mountsurface and extending substantially parallel to the direction ofdisplacement, and a rolling member fixed to the other end portions ofthe first and second leaf springs, wherein when the piezoelectricelement is displaced, the second leaf spring is displaced along thefirst leaf spring through the movable member to roll the rolling member.

According to a second aspect of the present invention, there is provideda device for magnifying displacement of a piezoelectric element adaptedto be displaced by application of voltage thereto, comprising a frameextending substantially parallel to a direction of displacement of thepiezoelectric element and mounting the piezoelectric element thereon, amovable member fixed to one end of the piezoelectric element withrespect to the direction of displacement, a first mount surface formedon the frame and extending substantially parallel to the direction ofdisplacement, a second mount surface formed on the movable member andextending substantially parallel to the direction of displacement, saidsecond mount surface being opposed to the first mount surface, a firstleaf spring mounted at its one end portion on the first mount surfaceand extending substantially parallel to the direction of displacement, asecond leaf spring mounted at its one end portion on the second mountsurface and extending substantially parallel to the direction ofdisplacement, and a rolling member fixed to the other end portions ofthe first and second leaf springs, wherein when the piezoelectricelement is displaced, the second leaf spring is displaced along thefirst leaf spring through the movable member to roll the rolling member,and wherein the first and second leaf springs include respectivedeformable portions facing to each other, and the deformable portionsare formed at their facing surfaces with respective non-contact portionsfor inhibiting contact between the deformable portions.

According to a third aspect of the present invention, there is providedin a device for magnifying displacement of a piezoelectric elementadapted to be displaced by application of voltage thereto, comprising aframe extending along the piezoelectric element and having a baseportion for supporting one end of the piezoelectric element with respectto a direction of displacement, a movable member fixed to the other endof the piezoelectric element, a pair of first and second leaf springseach fixed at one end portion to the frame and the movable member, and arolling member fixed to the other end portion of each of the leafsprings, wherein when the piezoelectric element is displaced, the leafsprings are deformed to roll the rolling member. The leaf springs areformed from a single spring member to define a split groove thereinextending from one end of the spring member toward the other endthereof, and the rolling member is integrally connected to the other endof the spring member.

According to a fourth aspect of the present invention, there is providedin a device for magnifying displacement of a piezoelectric elementadapted to be displaced by application of voltage thereto, comprising aframe extending along the piezoelectric element and having a baseportion for supporting one end of the piezoelectric element with respectto a direction of displacement, a movable member fixed to the other endof the piezoelectric element, a pair of first and second leaf springseach fixed at one end portion to the frame and the movable member, and arolling member fixed to the other end portion of each of the leafsprings, wherein when the piezoelectric element is displaced, the leafsprings are deformed to roll the rolling member. The first and secondleaf springs are formed with a small sectional area portion at a portionexcept the fixed ends of the leaf springs, said small sectional areaportion having a small sectional area in a direction substantiallyperpendicular to the direction of displacement of the piezoelectricelement smaller than a sectional area of the fixed ends.

According to a fifth aspect of the present invention, there is provideda device for magnifying displacement of a piezoelectric element adaptedto be displaced by application of voltage thereto, comprising a frameextending substantially parallel to a direction of displacement of thepiezoelectric element and mounting the piezoelectric element on a baseportion thereof, a movable member fixed to one end of the piezoelectricelement with respect to the direction of displacement, a first mountsurface formed on the frame and extending substantially parallel to thedirection of displacement, a second mount surface formed on the movablemember and extending substantially parallel to the direction ofdisplacement, said second mount surface being opposed to the first mountsurface, a first leaf spring mounted at one end portion on the firstmount surface and extending substantially parallel to the direction ofdisplacement, a second leaf spring mounted at one end portion on thesecond mount surface and extending substantially parallel to thedirection of displacement, and a rolling member fixed to the other endportion of each of the first and second leaf springs, wherein when thepiezoelectric element is displaced, the second leaf spring is displacedalong the first leaf spring through the movable member to roll therolling member, said device further comprising an elastically deformableconnecting member extending along the piezoelectric element on anopposite side of the frame with respect to the movable member andconnecting the movable member with a base portion of the frame, whereinwhen the piezoelectric element is displaced, the movable member isdisplaced substantially parallel to the direction of displacementagainst the elasticity of the connecting member to curve the second leafspring relative to the first leaf spring and thereby roll the rollingmember.

According to a sixth aspect of the present invention, there is provideda device for magnifying displacement of a piezoelectric element adaptedto be displaced by application of voltage thereto, comprising a frameextending substantially parallel to a direction of displacement of thepiezoelectric element and mounting the piezoelectric element on a baseportion thereof, a movable member fixed to one end of the piezoelectricelement with respect to the direction of displacement, a first mountsurface formed on the frame and extending substantially parallel to thedirection of displacement, a second mount surface formed on the movablemember and extending substantially parallel to the direction ofdisplacement, said second mount surface being opposed to the first mountsurface, a first leaf spring mounted at one end portion on the firstmount surface and extending substantially parallel to the direction ofdisplacement, a second leaf spring mounted at one end portion on thesecond mount surface and extending substantially parallel to thedirection of displacement, and a rolling member fixed to the other endportion of each of the first and second leaf springs, wherein when thepiezoelectric element is displaced, the second leaf spring is displacedalong the first leaf spring through the movable member to roll therolling member, said device further comprising a four-hinged parallellink mechanism provided between the frame and the movable member formaintaining the parallelism of the movable member to the direction ofdisplacement of the piezoelectric element.

According to a seventh aspect of the present invention, there isprovided a method of producing a device for magnifying displacement of apiezoelectric element adapted to be displaced by application of voltagethereto, comprising a frame extending substantially parallel to adirection of displacement of the piezoelectric element and mounting thepiezoelectric element thereon, a movable member fixed to one end of thepiezoelectric element with respect to the direction of displacement, afirst mount surface formed on the frame and extending substantiallyparallel to the direction of displacement, a second mount surface formedon the movable member and extending substantially parallel to thedirection of displacement, said second mount surface being opposed tothe first mount surface, a first leaf spring mounted at one end portionon the first mount surface and extending substantially parallel to thedirection of displacement, a second leaf spring mounted at one endportion on the second mount surface and extending substantially parallelto the direction of displacement, and a rolling member fixed to theother end portion of each of the first and second leaf springs, whereinwhen the piezoelectric element is displaced, the second leaf spring isdisplaced along the first leaf spring through the movable member to rollthe rolling member, said method comprising a first step of forming themovable member integrally with the frame, through a connecting portionin such a manner as to define a space for inserting therein thepiezoelectric element between the movable member and a base portion ofthe frame, a second step of fixing the leaf springs to the frame and themovable member, and a third step of forming a separation groove in theconnecting portion to separate the movable member from the frame.

According to an eighth aspect of the present invention, there isprovided an impact dot printing head of a type to be driven by apiezoelectric element adapted to be displaced by application of voltagethereto, comprising a plurality of printing units each having a printingwire for printing dots onto a printing medium, a displacementtransmitting mechanism for transmitting displacement of thepiezoelectric element to the printing wire, and a frame for supportingthe piezoelectric element and the displacement transmitting mechanism,said frame extending in a direction of displacement of the piezoelectricelement; a first base plate for fixedly supporting one end of the framewith respect to the direction of displacement of the piezoelectricelement; a second base plate for fixedly supporting the other end of theframe with respect to the direction of displacement of the piezoelectricelement, said second base plate having a nose portion for supporting theprinting wire; a first fixing means for fixing the first base plate tothe frame; and a second fixing means for fixing the second base plate tothe frame, wherein at least one of the first and second fixing means isso arranged as to intersect the direction of displacement of thepiezoelectric element.

According to a ninth aspect of the present invention, there is providedan impact dot printing head of a type to be driven by a piezoelectricelement adapted to be displaced by application of voltage thereto,comprising a displacement transmitting mechanism for transmittingdisplacement of the piezoelectric element to a printing wire forprinting dots onto a printing medium; a base plate for supporting thepiezoelectric element; a wiring board fixed to the base plate forsupporting a feeder line to be electrically connected to a lead wireconnected to the piezoelectric element; and a holder having acylindrical portion to be engaged with an outer periphery of thepiezoelectric element and a leg portion extending from one end of thecylindrical portion toward the wiring board, said leg portion having athroughhole for inserting the lead wire.

The invention will be more fully understood from the following detaileddescription and appended claims when taken with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a preferred embodiment of theprinting head according to the present invention;

FIG. 2 is a side view as viewed from the arrow II in FIG. 1.

FIG. 3 is a perspective view of a printing unit installed in theprinting head shown in FIG. 1;

FIG. 4 is an elevational view in partial section of the printing unitshown in FIG. 3;

FIG. 5 is a plan view of FIG. 3;

FIG. 6 is a perspective view of a modification of the printing unit;

FIG. 7 is an enlarged elevational view of the essential part of theprinting unit shown in FIG. 3;

FIG. 8 is a perspective view of one of the leaf springs shown in FIG. 7;

FIG. 9 is a perspective view of a modification of the printing unit;

FIG. 10 is an elevational view of FIG. 9;

FIG. 11 is a perspective view of the leaf springs shown in FIG. 9;

FIG. 12 is an elevational view of FIG. 11;

FIG. 13 is an elevational view of a modification of FIG. 12;

FIG. 14 is an elevational view of another modification of FIG. 12;

FIG. 15 is an exploded perspective view of a further modification ofFIG. 12;

FIG. 16 is a perspective view of a modification of the printing unit;

FIG. 17 is an elevational view of FIG. 16;

FIG. 18 is a perspective view of the leaf springs shown in FIG. 16;

FIG. 19 is an elevational view of FIG. 18;

FIG. 20 is a perspective view of a modification of FIG. 18;

FIG. 21 is a perspective view of another modification of FIG. 18;

FIG. 22 is a perspective view of a further modification of FIG. 18;

FIGS. 23 to 26 are elevational views of the printing unit, illustratingeach step of the producing method according to the present invention;

FIGS. 27 and 28 are elevational views similar to FIGS. 23 to 26,illustrating each step of a modification of the producing methodaccording to the present invention;

FIG. 29 is a partial elevational view of the essential part of FIG. 10;

FIG. 30 is a perspective view of a modification of the printing unit;

FIG. 31 is an elevational view of FIG. 30;

FIG. 32 is a partial elevational view of FIG. 31;

FIG. 33 is a partial elevational view of a modification of FIG. 31;

FIG. 34 is a perspective view of a modification of the printing unit;

FIG. 35 is an elevational view of FIG. 34;

FIG. 36 is a perspective view of the parallel link mechanism shown inFIG. 34;

FIG. 37 is an elevational view of a modification of FIG. 34;

FIG. 38 is an exploded perspective view of the essential part of anothermodification of FIG. 34;

FIG. 39(A) is a schematic elevational view of the conventional devicefor magnifying displacement of a piezoelectric element, illustrating aninoperative condition; and

FIG. 39(B) is a view similar to FIG. 39(A), illustrating an operativecondition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will now be described some preferred embodiments of the presentinvention with reference to the drawings.

Referring to FIGS. 1 and 2 which show a printing head in verticalsection and side, respectively, a head body 40 primarily consists offirst and second substantially rectangular base plates 42 and 44 opposedto each other at a predetermined distance, and four posts 46 connectingthe base plates 42 and 44 at the four corners thereof.

A plurality of (twenty four, for example) printing units 48 are providedbetween the first and second base plates 42 and 44 in such a manner asto be arranged on a circle concentric with a common center line of boththe base plates 42 and 44.

The second base plate 44 is formed with a substantially circular plateportion 49 disposed along the printing units 48, and with a hollow noseportion 54 extending outward from the plate portion 49. The nose portion54 includes a plurality of guide plates 52 for guiding the movement ofeach printing wire 50 connected to each printing unit 48. A supportmember 56 is provided on the inner surface of the second base plate 44to position and support each printing unit 48. The support member 56primarily consists of a circular support plate 58 disposed along theinner surface of the second base plate 44 and a plurality of partitionwalls 60 radially extending inward from the support plate 58 in such amanner that each partition wall 60 is interposed between the adjacentprinting units 48. The partition walls 60 are integrally formed with asupport ring 64 for supporting the outer surface of each frame 62 of theprinting units 48. The support plate 58 is formed at its central portionwith a central hole 66 which communicated with the axial hole of thenose portion 54. A plurality of guide pins 70 project from the innersurface of the support plate 58 in such a manner as to be arrangedaround the central hole 66, for guiding each wire driving arm 96 of theprinting units 48.

Referring to FIGS. 3, 4 and 5, each printing unit 48 includes apiezoelectric element 72.Iadd., one type of electro-distortion element,.Iaddend.adapted to be expanded and contracted by the application ofvoltage thereto and a displacement transmitting mechanism 74 adapted tomagnify the expansion and contraction of the piezoelectric element 72and transmit such a magnified displacement to the printing wire 50. Thepiezoelectric element 72 and the displacement transmitting mechanism 74are supported by the frame 62.

The frame 62 is formed of a metal plate having a predetermined thicknessand an elongated shape in such a manner as to extend substantiallyparallel to the displacement direction of the piezoelectric element 72.The frame 62 is formed at its lower end with a laterally extending baseportion 78 for supporting one end of the piezoelectric element 72through a temperature compensation member 76.

The piezoelectric element 72 is formed by a stack of piezoelectricceramics adapted to be expanded and contracted in the direction of thestack (in the longitudinal direction of the piezoelectric element 72).The temperature compensation member 76 is fixed to one end surface ofthe piezoelectric element 72 by an adhesive or the like. Thepiezoelectric element 72 is supported through the temperaturecompensation member 76 on a support surface 80 of the support portion78.

A rectangular movable member 82 is fixed to the other end surface of thepiezoelectric element 72 by an adhesive or the like. The movable member82 has a side surface opposed to an upper side surface of the frame 62with a given spacing defined therebetween. The given spacing is filledwith a pair of first and second leaf springs 84 and 86.Iadd., which areelastic, resilient members, .Iaddend.to be fixed to spring mountingsurfaces 88 and 90 of the frame 62 and the movable member 82,respectively. The spring mounting surfaces 88 and 90 are flat surfacesextending substantially parallel to the displacement direction of thepiezoelectric element 72. The spring mount surface 90 of the movablemember 82 is located at an end surface of the movable member 82 offsetfrom a center line of the piezoelectric element 72 to the frame 62.

The first leaf spring 84 has a side surface .Iadd.or connecting portion.Iaddend.entirely fixed by brazing or the like to the spring mountingsurface 88 of the frame 62, while the second leaf spring 86 has a sidesurface .Iadd.or connecting portion .Iaddend.entirely fixed by brazingor the like to the spring mounting surface 90 of the movable member 82.The second leaf spring 86 is movable relative to the first leaf spring84 under the condition where the opposed surfaces of both the leafsprings 84 and 86 are in contact.

The first and second leaf springs 84 and 86 extend upward by a givenlength from the upper ends of the spring mounting surfaces 88 and 90along the displacement direction of the piezoelectric element 72. Arolling member 92 is fixed to the upper ends of the first and secondleaf springs 84 and 86. The rolling member 92 primarily consists of abase member 94 having a high rigidity and a lightweight wire driving arm96 connected to the base member 94.

The base member 94 of the rolling member 92 is formed at its lowersurface with a horizontal recess 98 for receiving the upper ends of thefirst and second leaf springs 84 and 86. The surfaces (back surfaces)opposite the facing surfaces of the leaf springs 84 and 86 are fixed bybrazing to the inner surface of the recess 98. The base member 94 isfurther formed at its front surface with a vertical recess 100 forreceiving the base portion of the wire driving arm 96. The base portionis fixed in the vertical recess 100 by brazing. The printing wire 50 isfixed at its one end to the front end of the wire driving arm 96 bybrazing.

In order to move the movable member 82 parallel to the displacementdirection of the piezoelectric element 72, there is provided anelastically deformable .Iadd.restricting or .Iaddend.connection member104 between the frame 62 and the movable member 82. The connectionmember 104 extends vertically along the displacement direction of thepiezoelectric element 72 on the opposite side of the frame 62 withrespect to the piezoelectric element 72. A lower end portion of theconnection member 104 is fixed to an end surface of the base portion 78of the frame 62 .Iadd.which functions as a connection part.Iaddend.,while an upper end portion of the connection member 104 is fixed to afront end surface of the movable member 82 .Iadd.or connection part.Iaddend.on the opposite side of the second leaf spring 86.

The connection member 104 is formed of a thin-walled planar materialhaving a width in a plane parallel to the side surface of the frame 62.This arrangement.[.,.]. of the connection member 104 contributes toensuring a high rigidity of the connection member 104 in a rollingdirection of the movable member 82 rolled by a reaction force of theleaf spring 86. Further, an elastic force of the connecting member 104is set so that the moving force of the movable member 82 due to theexpansion of the piezoelectric element 72 may be applied substantiallyuniformly to the leaf spring 86 and the connection member 104. That is,the elastic force of the connection member 104 is set to be smaller thanthat of the leaf spring 86. For example, the ratio of the elastic forcesof the connection member 104 and the leaf spring 86 is set to be about1:1.5 under the unoperational condition of the piezoelectric element 72.This is due to the fact that when the leaf spring 86 is curved by theupward movement of the movable member 82, a substantially verticalcomponent (a component in the displacement direction of thepiezoelectric element 72) of the elastic force of the leaf spring 86 isrequired to be equal to the elastic force of the connection member 104under the operational condition. Therefore, the elastic force of theconnection member 104 is set to be smaller than that of the leaf spring86. If the elastic force of the connection member 104 is greater thanthat of the leaf spring 86 under the operational condition of thepiezoelectric element 72, the movable member generates a clockwisemoment to hinder smooth vertical motion of the movable member 82 andalso badly affect smooth expansion of the piezoelectric element 72.Thus, the provision of the connection member 104 contributes tosubstantially prevent the inclination of the movable member 82.

A back stopper 106 formed of low elastic rubber is fixed at an upper endof the connection member 104, so that when the rolling member 92 isrolled and returned, the lower edge of the wire driving arm 96 abutsagainst the upper surface of the back stopper 106. The back stopper 106is formed with a recess 108 for receiving the upper end portion of theconnection member 104, and is further formed with a side hole 110 forfilling an adhesive therethrough into the recess 108. Thus, the backstopper 106 is fixed to the connection member 104 by the adhesive.

The temperature compensation member 76 bonded to the lower surface ofthe piezoelectric element 72 functions to compensate the expansion orcontraction of the piezoelectric element 72 due to a peripheraltemperature change and thereby maintain constant the height from thesupport surface 80 of the base portion 78 of the frame 62 to the upperend of the piezoelectric element 72.

A thrust pin 112 is fitted into the base portion 78 for supporting thelower surface of the temperature compensation member 76, and is thenfixed integrally with the base portion 78 by means of beam welding. Thethrust pin 112 operates to slightly upwardly thrust the lower surface ofthe temperature compensation member 76 on the support surface 80,thereby applying the spring forces of the connection member 104 and thesecond leaf spring 86 to the piezoelectric element 72 at all times.

Lead wires 114 and 116 each connected at respective ends to bothelectrodes of the piezoelectric element 72 of each printing unit 48, andare welded at their respective opposite ends to by welding feeder lines122 by welding. The feeder lines 122 are supported on a wiring plate 120formed of an electrical insulator material. The wiring plate 120 isfixed to the outer surface of the first base plate 42. The lead wires114 and 116 are supported on a holder 118 formed of an electricalinsulator material.

Each holder 118 is primarily composed of a rectangular cylindricalportion 124 surroundingly engaged with the outer periphery of thepiezoelectric element 72 and a leg portion 128 extending from one sideof the cylindrical portion 124 through a hole 126 formed through thefirst base plate 42 to the inner surface of the wiring plate 120. Theleg portion 128 of the holder 118 is formed on one side surface with apair of guide channels 130 and 132 for guiding and supporting the leadwires 114 and 116 led out from both the electrodes of the piezoelectricelement 72 toward the wiring plate 120. The leg portion 128 is furtherformed at its lower end with a projection 134 projecting from the oneside surface of the leg portion 128. The projection 134 has a pair ofguide holes 136 and 138 coaxially .[.communication.]..Iadd.communicating .Iaddend.with the guide channels 130 and 132. Thewiring plate 120 also has a pair of guide holes 140 and 142 coaxiallycommunicating with the guide holes 136 and 138 of the projection 134.Thus, the lead wires 114 and 116 guided by the guide channels 130 and132 pass through the guide holes 136 and 138 of the projection 134 andthe guide holes 140 and 142 of the wiring plate 120. Then, the leadwires 114 and 116 from the guide holes 140 and 142 are connected bysoldering to the feeder lines 122.

The rectangular cylindrical portion 124 is formed at its lower end onthe opposite side of the leg portion 128 with a downward projection 143bonded at its lower end to the temperature compensation member 76, so asto support the cylindrical portion 124. The cylindrical portion 124 isloosely fitted around the piezoelectric element 72 so as not to hinderthe expansion and contraction of the piezoelectric element 72. Thefeeder lines 122 on the wiring plate 120 are supplied with a signalcorresponding to print data from a control circuit.

Referring back to FIG. 1, the inner surface of the first base plate 42is defined as a reference surface F, and one end surface of the frame 62of each printing unit 48 is brought into abutment against the referencesurface F. Then, a tightening screw 144 is threadly inserted from theouter surface of the first base plate 42 in a direction parallel to thedisplacement direction of the piezoelectric element 72 into one endportion of the frame 62, thus fixing the one end portion of the frame 62to the first base plate 42.

The circular plate portion 49 of the second base plate 44 is formed atits outer periphery on the inner surface thereof with a plurality ofmounting projections 148 projecting inwardly perpendicularly therefrom.Each projection 148 has a hole 150 elongated in a direction parallel tothe displacement direction of the piezoelectric element 72. A tighteningscrew 146 is inserted through each hole 150 of the projection 148 in adirection instersecting the displacement direction, preferably in adirection perpendicular thereto, and is threaded into a mountingprojection 152 projecting outwardly from the other end surface of theframe 62, thus fixing the other end portion of the first base plate 44.

In this preferred embodiment, the support posts 46 of the head body 40,the frames 62 and the connection members 104 of the printing units 48are formed of a material having the same coefficient of linear thermalexpansion, so as to cope with a temperature change.

In operation, when a print data signal is outputted from the controlcircuit to each printing unit 48 to apply voltage across both theelectrodes of the piezoelectric element 72, the piezoelectric element 72is expanded by a fixed length in the direction of stack of the ceramics,namely, in the direction of arrow X shown in FIG. 4 to thereby lift themovable member 82. As a result, the second leaf spring 86 receives themoving force of the movable member 82, and is accordingly lifted alongthe first leaf spring 84. At this moment, the second leaf spring 86 iselastically deformed to be curved between the movable member 82 and thebase portion 94 of the rolling member 92. Such an elastic deformation ofthe second leaf spring 86 generates a moment in the direction of arrow Pshown in FIG. 4. As a result, the first leaf spring 84 is slightlyelastically deformed, and simultaneously the rolling member 92 isrolled, so that the printing wire 50 connected at the tip of the rollingmember 92 is driven to advance as being guided by the guide plates 52.Accordingly, an end of the printing wire 50 is forced against a printingribbon (not shown), thus carrying out printing. In this preferredembodiment, the opposed surfaces of the first and second leaf springs 84and 86 contact with each other. As compared with the case that the firstand second leaf springs 84 and 86 were spaced a certain distance fromeach other, the preferred embodiment can provide a greater magnificationof expansion of the piezoelectric element 72 owing to the abovearrangement of the leaf springs 84 and 86. Accordingly, a requisitestroke of the printing wire 50 can be sufficiently provided.

When the voltage applied to the piezoelectric element 72 is cut off, thepiezoelectric element 72 under the expanded condition is returned to itsoriginal condition. Then, the movable member 82, the leaf springs 84 and86 and the rolling member 92 are all returned to their originalcondition, thus retracting the printing wire 50 to its originalposition.

As mentioned above, the flat surfaces of the first and second leafsprings 84 and 86 are fixed by brazing or the like to the flat springmounting surfaces 88 and 90 of the frame 62 and the movable member 82.Therefore, large fixing areas between the frame 62 and the first leafspring 84 and between the movable member 82 and the second leaf spring86 may be provided to thereby ensure a strong and stable fixedcondition. Furthermore, as the volumes of the frame 62 and the movablemember 82 are large, these members may be of large rigidity.

Further, the base portion 94 of the rolling member 92 as fixed to therespective end portions of the first and second leaf springs 84 and 86has a width substantially the same as that of the leaf springs 84 and86, and has a large volume, so that the base portion 94 may also be oflarge rigidity. Owing to the large rigidity of the frame 62, the movablemember 82 and the base portion 94 of the rolling member 92, the leafsprings 84 and 86 are deformed at a limited portion among the frame 62,the movable member 82 and the base portion 94, thereby suppressing areduction in displacement magnification rate. Moreover, excess vibrationof the leaf springs 84 and 86, the frame 62, the movable member 82 andthe base portion 94 may be eliminated to thereby reduce the time untilstoppage of the rolling member 92 including the wire supporting arm 96,that is, to increase a natural frequency of the whole movable elementincluding the rolling member 92, the leaf springs 84 and 86, etc. As aresult, a high-speed operation of the rolling member 92 may be achieved.

Furthermore, in this preferred embodiment, as the end surface of thebase portion 78 of the frame 62 and the end surface of the movablemember 82 opposite the second leaf spring 86 are connected to each otherby means of the elastically deformable connection member 104, the movingforce of the movable member 82 generated by the expansion of thepiezoelectric element 72 is substantially uniformly received by thesecond leaf spring 86 and the connection member 104. Accordingly, themovable member 82 may be moved in a direction parallel to thedisplacement direction of the piezoelectric element 72, therebypreventing the generation of a bending moment in the piezoelectricelement 72. Therefore, in spite of the fact that the piezoelectricelement 72 is formed of piezoelectric ceramics which are less resistantagainst a bending stress, the piezoelectric element 72 may be preventedfrom being damaged to thereby improve the durability.

In installing each printing unit 48 into the head body 40, the printingunit 48 is first inserted into the adjacent partition walls 60 of thesupporting member 56 on the second base plate 44, and is thentemporarily mounted at one end to the second base plate 44 by means ofthe tightening screw 146. Then, the first base plate 42 is mounted tothe printing unit 48 in such a manner that the other end of the frame 62abuts against the reference surface F of the first base plate 42, and isfixed to the printing unit 48 by tightening the screw 144 in a directionparallel to the displacement direction of the piezoelectric element 72.Thereafter, the screw 146 is tightened in a direction perpendicular tothe displacement direction of the piezoelectric element 72 to fix theframe 62 at the mounting portion 152 to the second base plate 44. Thus,the frame 62 of each printing unit 48 is fixed at both ends to the firstand second base plates 42 and 44. As compared with devices in whichtightening means (bolts or screws) are tightened in a direction parallelto the displacement direction of the piezoelectric element 72 to fix theframe 62 to the first and second base plates 42 and 44, this preferredembodiment may reduce the dispersion in mounting position of the frame62 with respect to the displacement direction of the piezoelectricelement 72. Further, the tightening forces of the screws 144 and 146 donot operate to expand the frame 62 in the displacement direction of thepiezoelectric element 72, thereby preventing the expansion of the frame62 upon tightening of the screws 144 and 146.

As mentioned above with reference to FIGS. 3 and 4, the lead wires 114and 116 connected to both the electrodes of each piezoelectric element72 are guided through the guide channels 130 and 132 of the leg portion128 of the holder 118, and are inserted through the holes 136 and 138 ofthe leg portion 128 and through the holes 140 and 142 of the wiringplate 120. Then, each end of the lead wires 114 and 116 is connected bysoldering to the feeder lines 122 on the wiring plate 120. With thisarrangement, it is possible to prevent interference or entanglementbetween the lead wires 114 and 116 and make the soldering work easy.Further, it is also possible to prevent the lead wires 114 and 116 frombeing erroneously soldered to the electrodes of the piezoelectricelement 72.

In this embodiment, the frame 62, the connection member 104 and themovable member 82 are formed independently, and are then integrallyfixed together by brazing or the like. Therefore, the supporting surface80 of the base portion 78 of the frame 62 and the fixing surface of themovable member 82 to the piezoelectric element 72 may be easily finishedwith a high accuracy. Accordingly, the displacement of the piezoelectricelement 72 upon application of voltage thereto may be reliablytransmitted to the movable member 82 and the second leaf spring 86.Alternatively, the frame 62, the connection member 104 and the movablemember 82 may be integrally formed from a single metal plate.

Further, the first base plate 42 may be formed at its outer periphery onthe inner surface with a perpendicular projection for threadedlyinserting thereinto the tightening screw 144 in a directionperpendicular to the displacement direction of the piezoelectric element72. As to the tightening screw 146 on the second base plate 44 side, thescrew 146 may be tightened in a direction either perpendicular orparallel to the displacement direction of the piezoelectric element 72.

As shown in FIG. 6, the holder 118 shown in FIG. 3 may be removed. Inthis case, the lead wires 114 and 116 are directly led to the feederlines 122 on the wiring plate 120.

Although it is preferable to contact the leaf springs 84 and 86 for thepurpose of increasing the displacement magnifying rate to the maximum asassociated with the expansion of the piezoelectric element 72, the leafsprings 84 and 86 may be spaced a small distance.

FIG. 8 shows an expanded perspective view of the leaf spring 84(86).Both the leaf springs 84 and 86 are formed from a rectangular elasticplate having uniform thickness and width. As shown in FIG. 7, uponapplication of voltage to the piezoelectric element 72, the leaf spring86 fixed to the movable member 82 is upwardly displaced in parallel tothe leaf spring 84 fixed to the frame 62. At the same time, both theleaf springs 84 and 86 are elastically deformed to generate a stresstherein. The stress tends to be concentrated at an fixed edge of theleaf springs 84 and 86, e.g., near the point 0 shown in FIG. 7.

Referring next to FIGS. 9 to 12 which show a second preferred embodimentintending to reduce such a stress concentration in the first preferredembodiment and improve the durability of the leaf springs. In the secondpreferred embodiment, the same or like parts as in the first preferredembodiment are designated by the same reference numerals, and therelated explanation will be omitted.

As shown in FIGS. 9 and 10, a second leaf spring 156 fixed to themovable member 82 is adapted to be displaced in parallel to a first leafspring 154 fixed to the frame 62 upon expansion of the piezoelectricelement 72, resulting in rolling of the rolling member 92. The leafsprings 154 and 156 are constructed in such a manner that a sectionalarea in a direction perpendicular to the displacement direction isreduced at an intermediate position of the displacement direction. Thatis, as clearly shown in FIGS. 11 and 12, the first and second leafsprings 154 and 156 are formed on their side surfaces opposite to thefacing surfaces with sectional U-shaped grooves 158 and 160 extendingacross the width W of the leaf springs, respectively. As a result, thereare formed thin-walled portions 162 and 164 at the positions of thegrooves 158 and 160 of the first and second leaf springs 154 and 156. Inother words, the first leaf spring 154 has a large sectional area at thefixed portions fixed to the frame 62 and the rolling member 92, but hasa small sectional area at the thin-walled portion 162, namely, at theelastically deformable portion. Similarly, the second leaf spring 156also has a large sectional area at the fixed portions fixed to themovable member 82 and the rolling member 92, but has a small sectionalarea at the thin-walled portion 164.

When the second leaf spring 156 is displaced in a directionsubstantially parallel to the first leaf spring 154 upon expansion ofthe piezoelectric element 72, and both the leaf springs 154 and 156 areelastically deformed, the stress is primarily applied to the thin-walledportions 162 and 164 having a small sectional area, thereby greatlyreducing the stress to be applied to the upper and lower fixed (brazed)edges of the leaf springs 154 and 156, e.g., at the point 0 shown inFIG. 12. Accordingly, it is possible to prevent the generation ofcracking at the fixed edges due to repeated elastic deformation of theleaf springs 154 and 156 and thereby improve the durability.

In accordance with CAEDS (tradename of structure analysis softwareproduced by International Business Machines Corporation), the presentinventors have investigated to calculate the stresses to be applied atthe points 0, P and Q of the leaf springs 154 and 156 shown in FIG. 12and the stresses to be applied at the points O, P and Q of the leafsprings 84 and 86 shown in FIG. 7 as having the uniform width andthickness. The result of calculation is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Conditions                                                                    Rate of Mag-   Natural      Stress (kg/mm.sup.2)                              nification (%) Frequency (KHz)                                                                            O      P    Q                                     ______________________________________                                        Example of                                                                    FIG. 12 230        2.5          7.6  54.9 56.2                                Example of                                                                    FIG. 7  230        2.5          14.4 50.6 51.2                                ______________________________________                                    

The dimensions of the leaf springs 154 and 156 shown in FIG. 12 and theleaf springs 84 and 86 shown in FIG. 7 are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        W(mm)        t(mm)   L(mm)   D(mm) E(mm) F(mm)                                ______________________________________                                        Example of                                                                    FIG. 12 4.0      0.8     1.2   0.8   0.52  0.28                               Example of                                                                    FIG. 7  4.0      0.28    0.8   --    --    --                                 ______________________________________                                    

Where the characters, W, t, L, D, E and F stand for a width of each leafspring, a thickness of each leaf spring, a vertical distance of theunfixed portion of each leaf spring, a width of the U-shaped groove, adepth of the U-shaped groove and a thickness of the thin-walled portion,respectively.

As is apparent from Table 1, the stress at the point 0 in Example ofFIG. 12 is made substantially half the stress at the point 0 in Exampleof FIG. 7.

Referring to FIG. 13 which shows a modification of the embodiment shownin FIGS. 9 to 12, the first leaf spring 154 is formed on its outer sidesurface with three U-shaped grooves 166, 168 and 170 extending acrossthe width of the leaf spring 154 and arranged in uniformly spacedrelationship from each other in the displacement direction of the leafspring 154. The central groove 168 has a depth greater than the othergrooves 166 and 170. Similarly, the second leaf spring 156 is formed onits side surface opposite to the outer side surface of the first leafspring 154 with three U-shaped grooves 172, 174 and 176 similar to theU-shaped grooves 166, 168 and 170. With this arrangement, the stress isprevented from being concentrated at the thin-walled portionscorresponding to the central deep grooves 168 and 174, and may bedispersed to the other thin-walled portions corresponding to the shallowgrooves 166, 170, 172 and 176.

Referring to FIG. 14 which shows another modification of the embodimentshown in FIGS. 9 to 12, the first leaf spring 154 is formed on its outerside surface with a pair of U-shaped grooves 178 and 180 extendingacross the width of the leaf spring 154 and arranged in given spacedrelationship from each other in the displacement direction of the leafspring 154. The grooves 178 and 180 have the same width and depth.Similarly, the second leaf spring 156 is formed on its side surfaceopposite to the outer side surface of the first leaf spring 154 with apair of U-shaped grooves 182 and 184 similar to the grooves 178 and 180.With this arrangement, the stress is substantially uniformly dispersedto the thin-walled portions formed between the grooves 178, 182 and 180,184.

Referring to FIG. 15 which shows a further modification, the first andsecond leaf springs 154 and 156 have a uniform thickness, but have areduced width at their intermediate portions 186. Further, each leafspring 154(156) is formed at its upper and lower fixed ends withrecesses 188 and 190 to be engaged with projections 194 of the baseportion 94 of the rolling member 92 and projections 192 and 196 of theframe 62 and the movable member 82, respectively. With this arrangement,the first and second leaf springs 154 and 156 are positioned at theirfixed end portions adjacent to the groove 98 of the rolling member 92,the mounting surface 88 of the frame 62 and the mounting surface 90 ofthe movable member 82, and are fixed by brazing thereto. Further, aseach leaf spring has intermediate small-width portions 186, the stressmay be prevented from being concentrated at the fixed edge of each leafspring.

In the first and second preferred embodiments as mentioned above, thefirst and second leaf springs 84 and 86 or 154 and 156 are so arrangedas to extend in parallel to the displacement direction of thepiezoelectric element 72 under the condition where the facing surfacesof each leaf spring are in contact with each other. Upon expansion ofthe piezoelectric element 72, the movable member 82 is displaced toupwardly move the leaf spring 86(156) fixed to the movable member 82 insuch a manner as to slidingly contact the leaf spring 84(154) fixed tothe frame 62. At the same time, both the leaf springs 84 and 86 (154 and156) are elastically deformed. In such a structure, the leaf springs 84and 86 (154 and 156) are installed into the groove 98 of the baseportion 94 of the rolling member 92 in such a manner that the lower endsof the leaf springs tend to be curved outwardly. Further, the leafspring 86(156) is fixed to one side surface of the movable member 82. Asa result, it was realized in the experiment that the deformable portionsof the leaf springs are wavingly slid with a large frictional force,causing a possibility of wear or seizure of the leaf springs.

FIGS. 16 to 22 show a third preferred embodiment intended to reduce suchlarge friction at the deformable portions of the leaf springs contactingwith each other and thereby prevent the wear or seizure of the leafsprings.

Referring to FIGS. 16 to 19 which show a third preferred embodiment, apair of upper and lower wedge members 198 and 200 are interposed betweenthe lower end surface of the piezoelectric element 72 and the upper endsurface of the base portion 78 of the frame 62. Both the wedge members198 and 200 are formed of a material such as zinc having a linearexpansion characteristic contrary to that of the piezoelectric element72, so that the expansion and contraction of the piezoelectric element72 due to a temperature change may be compensated by the contraction andexpansion of the wedge members 198 and 200 to thereby maintain constantthe height of the piezoelectric element 72 from the upper end surface ofthe base portion 78 of the frame 62.

Similar to the previous preferred embodiments, the first and second leafsprings 204 and 206 contacting with each other are formed with U-shapedgrooves 158 and 160 to form thin-walled portions (deformable portions)162 and 164, respectively. The thin-walled portions 162 and 164 arereadily deformable.

The opposed surfaces of the deformable portions 162 and 164 of the leafsprings 204 and 206 are formed with recessed portions 208 ad 210 forhindering contact between the deformable portions 162 and 164. Therecessed portions 208 and 210 extend across the width of the leafsprings 204 and 206 on the opposite side of the grooves 158 and 160,thus defining a rectangular cavity between the deformable portions 162and 164.

When the second leaf spring 206 fixed to the movable member 82 isupwardly moved along the first leaf spring 204 fixed to the frame 62,and the deformable portions of the leaf springs 204 and 206 areelastically deformed, the frictional force to be generated between thedeformable portions is reduced by the provision of the recessed portions208 and 210. Accordingly, it is possible to prevent the generation ofwear or seizure between the deformable portions 162 and 164 and welltransmit the displacement of the movable member 82 in receipt of theexpansion of the piezoelectric element 72. As a result, both the leafsprings 204 and 206 are deformed duly by a given quantity at thedeformable portions 162 and 164, respectively. Accordingly, the rollingmember 92 is rolled by a given angle to thereby greatly magnify theexpansion of the piezoelectric element 72 and transmit the magnifiedexpansion to the printing wire 50.

The inventors have investigated to compare the natural frequencies ofthe movable portion consisting of the leaf springs 154 and 156 and therolling member 92 shown in FIG. 12 and the movable portion consisting ofthe leaf springs 204 and 206 and the rolling member 92 shown in FIG. 19,and also compare the strokes of the printing wire 50 between FIG. 12 andFIG. 19. The results of comparison is shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    W          t   l   t2  S   l 2 N   P                                          (mm)       (mm)                                                                              (mm)                                                                              (mm)                                                                              (mm)                                                                              (mm)                                                                              (KHz)                                                                             (μm)                                    __________________________________________________________________________    Example of                                                                    FIG. 19                                                                             4.0  0.8 1.0 0.2 0.2 1.2 2.1 380                                        Example of                                                                    FIG. 12                                                                             4.0  0.8 1.0 0.27                                                                              --  --  2.7 227                                        __________________________________________________________________________

Where W and t stand for a width and a thickness of the leaf spring,respectively; l and t2 stand for a length and a wall thickness of thedeformable portion, respectively; S and l2 stand for a spacing and alength of the cavity defined by the recessed portion; and N and P standfor the natural frequency and the stroke of the wire 50. The leafsprings 154 and 156 were used in the test under an initial conditionwhere seizure and wear have not yet been generated.

As is apparent from Table 3, since the deformable portions 162 and 164of the leaf springs 204 and 206 shown in FIG. 19 are formed with therecessed portions 208 and 210 defining a cavity with a spacing of 0.2mm, a frictional force between the facing surfaces of the deformableportions 162 and 164 may be greatly reduced to thereby increase thedisplacement magnification rate (a percentage of the stroke of theprinting wire 50 relative to the expansion quantity of the piezoelectricelement 72). As a result, the seizure and wear generated between thefacing surfaces of the deformable portions 162 and 164 may be preventedto maintain the increased magnification rate for a long period of time.

It is noted that each dimension shown in Table 3 is merely exemplary,and may be modified as shown in Table 4 corresponding to the followingExamples 1 to 4.

In Example 1, the spacing S of the cavity defined by the deformableportions 208 and 210 was set to 0.6 mm, and the length of the cavity wasset to 1.0 mm. The other dimensions were identical with those of theembodiment shown in FIG. 19.

In Example 2 shown in FIG. 20, the deformable portions 162 and 164 ofthe leaf springs 204 and 206 have no grooves on opposite side surfacesthereof so as to increase the spacing S of the cavity defined by therecessed portions 208 and 210.

In Example 3 shown in FIG. 21, the structure is similar to that ofExample 2 except that a small spacing S2 is defined between the facingsurfaces of the leaf springs 204 and 206.

In Example 4 shown in FIG. 22, a single leaf spring 212 is provided tobe formed with a vertically extending U-shaped groove 213 at a laterallycentral portion thereof to result in the formation of a pair of leafspring portions 204 and 206. The U-shaped groove 213 functions as thecavity mentioned in the previous Examples 1 to 3. Table 4 shows thecomparison among the above Examples 1 to 4.

                                      TABLE 4                                     __________________________________________________________________________    W         t   l   t2  S   l2  S2  N   P                                       (mm)      (mm)                                                                              (mm)                                                                              (mm)                                                                              (mm)                                                                              (mm)                                                                              (mm)                                                                              (KHz)                                                                             (μm)                                 __________________________________________________________________________    Example 1                                                                           4.0 0.8 1.0 0.2 0.6 1.0 --  2.4 330                                     Example 2                                                                           4.0 0.8 1.0 0.27                                                                              1.06                                                                              1.0 --  4.2 210                                     Example 3                                                                           4.0 0.6 1.0 0.2 1.0 1.0 0.2 3.5 250                                     Example 4                                                                           4.0 0.5 1.0 0.2 0.6 --  --  2.4 330                                     __________________________________________________________________________

As apparent from Tables 3 and 4, the displacement magnification rate inthe embodiment shown in FIG. 19, Example 1 and Example 4 is increased incomparison with that in the embodiment shown in FIG. 12.

In the embodiment shown in FIG. 12, the spacing S is reduced to be zeroso as to increase the magnification rate in accordance with a principleof lever principles. However, a load to be applied to the piezoelectricelement 72 is increased to suppress the expansion of the piezoelectricelement 72, resulting in limitation of the stroke of the printing wire.To the contrary, in the embodiment shown in FIG. 19, Example 1 andExample 4, a distance between the center of the thickness of thedeformable portion 162 and the center of the thickness of the deformableportion 164 is set to 0.4-0.8 mm, so that although the magnificationrate is just reduced, the load to be applied to the piezoelectricelement 72 is reduced. Accordingly, it is considered that a large strokeof the printing wire could be obtained.

However, the distance between the centers of the thickness is furtherincreased as in Examples 2 and 3, the magnification rate is reduced, andthe stroke tends to be suppressed.

As to the natural frequency, an increase in the natural frequencycontributes to an increase in a return speed of the rolling member 92,resulting in an improvement in a printing speed of the printing head.Although the natural frequencies in Examples 1 and 4 are smaller thanthose in Examples 2 and 3, Examples 1 and 4 are preferred from theviewpoint of the stroke of the printing wire.

In the foregoing preferred embodiments, the frame 62 and the movablemember 82 are formed independently. In mounting the piezoelectricelement 72, the movable member 82 is positioned through the leaf springs84 and 86 (154 and 156 or 204 and 206) and the connecting member 104relative to the frame 62, and then the piezoelectric element 72 isfixedly interposed between the movable member 82 and the base portion 78of the frame 62. In connection with this, it is desirable to provide anaccurate dimension and a high degree of parallelism between the movablemember 82 and the base, portion 78 of the frame 62. That is, less errorduring installation of the movable member 82 is desired.

FIGS. 23 to 26 show a method of producing the printing unit whichimproves the accuracy of dimension and the degree of parallelism betweenthe movable member 82 and the base portion 78 of the frame 62 by way ofan example in accordance with the present invention.

Referring to FIG. 23, the frame 62 is formed from a rectangular metalplate having a given thickness extending in a direction substantiallyparallel to the piezoelectric element 72. The frame 62 is formed at itslower end portion with the laterally projecting base portion 78 forsupporting the lower end of the piezoelectric element 72 through thepair of wedge members 198 and 200. Further, the frame 62 is integrallyformed at its upper end portion with a movable member 214 connectedthrough a connecting portion 216. Thus, the movable member 214 is spaceda distance L from the base portion 78 so as to insert the piezoelectricelement 72 and the wedge members 198 and 200. A recess 218 is definedbetween the frame 62 and the movable member 214 so as to insert the baseportions of the leaf springs 154 and 156 by press working, for example.

The upper surface 80 of the base portion 78 of the frame 62 and thelower surface 220 of the movable member 214 are finished as required soas to further improve the accuracy of the distance L and the degree ofparallelism.

After the frame 62 and the movable member 214 are formed as mentionedabove, the upper end portions of the leaf springs 154 and 156 areinserted into the groove 98 of the base member 94 of the rolling member92, and are fixed by brazing thereto. Then, the base portions of theleaf springs 154 and 156 fixed to the base member 94 are inserted intothe recess 218, and are fixed by brazing to the inner wall surface ofthe recess 218. Under this condition, the leaf springs 154 and 156 areelastically deformably contacted with each other.

Then, the connecting member 104 adapted to be elastically displaced in adirection parallel to the displacement direction of the piezoelectricelement 72 is provided between the movable member 214 and the baseportion 78 of the frame 62 in such a manner that the upper end portionof the connecting member 104 is fixed to the side surface of the movablemember 214, while the lower end portion is fixed to the side surface ofthe base portion 78. In this embodiment, a sectional area at the endportions of the connecting member 104 to be fixed to the movable member214 and the frame 62 are larger than a sectional area at an intermediateportion between the fixed end portions, by forming three elongated holesat the intermediate portion, so that the connecting member 104 may bemore readily expanded and contracted in receipt of the displacement ofthe piezoelectric element 72.

After the leaf springs 154 and 156 and the supporting member 104 aremounted as mentioned above, a separation slit 222 is formed into theconnecting portion 220 from the underside to the bottom of the recess218, so as to separate the movable member 214 from the frame 62.

Thereafter, the upper wedge member 198 is fixed to the lower end surfaceof the piezoelectric element 72 by an adhesive, and they are insertedbetween the movable member 214 and the base portion 78 of the frame 62until a stopper surface 226 of the upper wedge member 198 abuts againstthe side surface of the frame 62, and then the upper end surface of thepiezoelectric element 72 abuts against the lower surface of the movablemember 214. At this time, the upper end surface of the piezoelectricelement 72 is bonded by an adhesive to the lower surface of the movablemember 214 as required.

Then, the lower wedge member 200 is inserted between the upper wedgemember 198 and the base portion 78 of the frame 62, and force isapplied, thus completing the installation of the piezoelectric element72. At this time, the abutting surfaces among the lower wedge member200, the upper wedge member 198 and the base portion 78 of the frame 62are coated with an adhesive as required.

In accordance with the above steps, the high accuracy of the distance L(shown in FIG. 25) and the parallelism between the base portion 78 ofthe frame 62 and the movable member 214 may be ensured. Accordingly, thepiezoelectric element 72 and the pair of wedge members 198 and 200 maybe closely fitted between the base portion 78 of the frame 62 and themovable member 214, and the movable member 214 may be displacedsufficiently in receipt of the displacement of the piezoelectric element72. Thus, both the leaf springs 154 and 156 are elastically deformedsufficiently in receipt of the displacement of the movable member 214 toaccurately roll the rolling member 92 at a given angle, thereby ensuringgood printing operation.

Referring to FIGS. 27 and 28 which show a modification of the preferredembodiment shown in FIGS. 23 to 26, wherein a single thick leaf spring212 is formed with a central split groove 213 extending from theseparation groove 222 formed at the connecting portion 216.

The printing unit in this case is manufactured in the following manner.That is, as shown in FIG. 27, the movable member 214 is integrallyformed at one end of the frame 62 through the connecting portion 216.Then, the single thick leaf spring 212 fixed to the rolling member 92 isinserted into the recess 218 formed between the frame 62 and the movablemember 214, and is fixed by brazing to the recess 218.

Thereafter, as shown in FIG. 28, the separation groove 222 is formed inthe connecting portion to separate the movable member 214 from the frame62. Further, the central split groove 213 is formed in the single leafspring 212 in such a manner as to extend from the separation groove 222,thereby forming a pair of leaf spring members 204 and 206.

According to this example, the high accuracy of the distance and theparallelism between the movable member 214 and the base portion 78 ofthe frame 62 can be obtained. Moreover, since the single leaf spring 212is used, the number of parts may be reduced.

In the foregoing preferred embodiments, the rolling member 92 is sofixed as to ride over the end portions of the pair of leaf springs. Insuch a structure as shown in FIG. 29, the upper end portions of the leafsprings 154 and 156 are fixed in the recess 98 of the base member 94 ofthe rolling member 92, and the lower end portions are fixed to themovable member 82 and the frame 62. Upon displacement of thepiezoelectric element 72, the deformation of the leaf springs 154 and156 on the base member 94 side is greater than that on the frame 62 andthe movable member 82 side, and a brazed portion A on the inner surfaceof the recess 98 is subjected to a repeated tensile load and compressionload. Thereafter, there is a possibility of cracks being generated atthe brazed portion A. If the cracks were generated, the leaf springs 154and 156 would be eventually separated from the base member 94 of therolling member 92.

The following preferred embodiment as shown in FIGS. 30 and 31 isintended to prevent the generation of cracks at the fixing portionbetween the leaf springs and the rolling member and thereby improve thedurability, and also to reduce the number of parts and thereby simplifythe structure.

Referring to FIGS. 30 and 31, a single thick spring member 230 is formedwith a central split groove 232 to thereby form a pair of leaf springs234 and 236. Further, a head portion connecting the leaf springs 234 and236 functions as a rolling base member 238. That is, the pair of splitplate portions of the spring member 230 function as the leaf springs 234and 236, while the head portion of the spring member 230 functions asthe rolling base member 238. In other words, the leaf springs 234 and236 are integrally formed with the rolling base member 238 with no fixedportions.

The leaf springs 234 and 236 are fixed by brazing to the spring mountingsurfaces 88 and 90 of the frame 62 and the movable member 214. Further,the leaf springs 234 and 236 are formed at their intermediate positionswith opposite U-shaped grooves 158 and 160 at which portions the leafsprings are mainly elastically deformed. The head portion 238 is formedwith a recess 240 for receiving the wire driving arm 96 of the rollingmember 228. Thus, the base end portion of the wire driving arm 96 isinserted into the recess 240, and is fixed by brazing to the recess 240.The printing wire 50 is also fixed by brazing to the tip of the wiredriving arm 96. In this embodiment, the frame 62 is formed independentlyof the movable member 214. In this regard, FIG. 32 shows a modificationof the preferred embodiment shown in FIGS. 30 and 31. In themodification shown in FIG. 32, the movable member 214 is integrallyformed with the frame 62, so that the high accuracy of the distance Land the parallelism between the base portion of the frame 62 and themovable member 214 may be readily attained. After the spring member 230is installed at the connecting portion 216 between the movable member214 and the frame 62, the separation groove 222 is formed in theconnecting portion 216 to separate the frame 62 and the movable member214. Further, the central split groove 232 is formed in the springmember 230 in such a manner as to extend from the separation groove 222.

As mentioned above, since the pair of leaf springs 234 and 236 and therolling base member 238 are integrally formed by the single springmember 230, there is no necessity for fixing (brazing) both the members,resulting in no possibility of the generation of cracks at the brazedportion, thus improving the durability. In addition, the number of partsmay be reduced.

Referring to FIG. 33 which shows a modification of the above preferredembodiments shown in FIGS. 30 to 32, a spring member 242 is bent in theform of a U-shape to form the pair of leaf springs 234 and 236. A bentportion or a head portion of the spring member 242 is fixed to a baseportion 244 (corresponding to the rolling base member) of the rollingmember 228 by welding or brazing.

In the displacement magnifying mechanism as mentioned in the foregoingpreferred embodiments shown in FIGS. 1 through 33, there is provided theelastically deformable .Iadd.restricting or .Iaddend.connecting member104 between the movable member 82 (as in FIG. 10, for example) and thebase portion 78 of the frame, so as to maintain parallel displacement ofthe movable member 82 in receipt of the displacement of thepiezoelectric element 72 and thereby prevent lack of the rolling angleof the rolling member 92. In this case, it is necessary to set theelastic force of the connecting member 104 so that it may be fullybalanced with the elastic force of the leaf springs 154 and 156.However, it is actually hard to precisely balance both the elasticforces under the dynamic condition of these members.

The following preferred embodiment as shown in FIGS. 34 through 38 isintended to prevent the inclination of the movable member 82 morereliably by providing a .Iadd.restricting member or .Iaddend.parallellink mechanism between the movable member 82 and the frame 62.

Referring first to FIGS. 34 to 36, the construction of the printing unitis similar to the preferred embodiment shown in FIG. 9, for example,except that a parallel link mechanism 246 is provided.

The parallel link mechanism 246 is provided between the frame 62 and themovable member 82 so as to guide the movable member 82 under thecondition parallel to the displacement direction of the piezoelectricelement 72. As clearly seen in FIG. 36, the parallel link mechanism 246is formed from an elastically deformable single plate by punching andbending, thus forming a pair of parallel link plates 248 having the sameshape and a connecting portion 250 connecting both the link plates 248.

Each of the pair of link plates 248 includes a pair of parallel verticallink portions 252 and 254, a pair of parallel horizontal link portions264 and 266 and four elastically deformable hinge portions 256, 258, 260and 262 connecting the vertical link portions 252 and 254 with thehorizontal link portions 264 and 266. Thus, the link plate 248 forms aquadri-hinged parallel link.

As shown in FIGS. 34 and 35, the opposed inner surfaces of the leftvertical link portions 252 of the link plates 248 are fixed by brazingto both the side surfaces of the frame 62, while the opposed innersurfaces of the right vertical link portions 254 are fixed by brazing toboth the side surfaces of the movable member 82 at its intermediateportion. Further, the inner surface of the connecting portion 250 of thelink mechanism 246 is fixed to the upper surface of the movable member82.

In operation, when the piezoelectric element 72 is supplied withvoltage, it is expanded by a predetermined length in the direction ofthe arrow X shown in FIG. 35 to displace the movable member 82 againstthe load of the connecting member 104, the second leaf spring 156 andthe parallel link mechanism 246. Then, the second leaf spring 156 islifted along the first leaf spring 154 by the displacement force of themovable member 82. As a result, both the leaf springs 154 and 156 arecurved like a bimetal to generate a moment in the direction of the arrowP shown in FIG. 35. Accordingly, the rolling member 92 is rolled toadvance the printing wire 50. To the contrary, when the voltage appliedto the piezoelectric element 72 is removed, the piezoelectric element 72is contracted to follow the displacement of the movable member 82 andthereby return the rolling member 92 and the printing wire 50 to theiroriginal position.

In driving the leaf spring 156 by the movable member 82, the inclinationof the movable member 82 due to the load of the leaf spring 156 issuppressed by the connecting member 104 connected to the movable member82, and it is further suppressed by the parallel link mechanism 246fixed so as to ride over the movable member 82 and the frame 62. Thatis, the movement of the movable member 82 is restricted by the linkplates 248, and is guided under the condition parallel to thedisplacement direction of the piezoelectric element 72. Accordingly, itis possible to eliminate lack of elastic deformation of the leaf springs154 and 156 due to the inclination of the movable member 82, therebyproviding a sufficient stroke of the printing wire 50.

The leaf springs 154 and 156 are formed with grooves 158 and 160 to formthin-walled deformable portions similar to the previous preferredembodiments. Additionally, the leaf springs 154 and 156 are formed withupper small grooves 268a and lower small grooves 268b, so as to ensurebrazing. That is, upon brazing, rod-like brazing members are insertedinto the small grooves 268a and 268b, and the same molten by applicationof heat is penetrated into a small gap between the contact surfacesamong the leaf springs, the movable member and the frame. Then, thebrazing material is hardened to complete the brazing.

Referring to FIG. 37 which shows a modification of the preferredembodiment shown in FIGS. 34 to 36, the horizontal link portions 264 and266 have a length greater than that in the previous preferred embodimentshown in FIGS. 34 to 36, and the other construction is similar to theprevious preferred embodiment. With this arrangement, the displacementof the movable member 82 may be made near a linear displacement inparallel to the displacement of the piezoelectric element 72.

Referring to FIG. 38 which shows a further modification, the pair ofleaf springs 234 and 236 are formed from a single thick spring member230 by defining the split groove 232, and the head portion of the springmember 230 forms the rolling base member 238 to be fixed to the wiredriving arm 96. This construction is substantially the same as thatshown in FIG. 30.

Reference numeral 272 designates a parallel link mechanism in thismodification. The vertical link portions 252 and 254 extend a fixedlength upward from the upper surfaces of the frame 62 and the movablemember 82. The vertical link portions 252 are fixed at their lowerportion to both the side surfaces of the frame 62, and are integrallyconnected at their upper portion with each other by a connecting portion250. In contrast to the constructions of the preferred embodiments shownin FIGS. 34 and 37 wherein the parallel link mechanisms 246 and 268 arelocated on one side of the leaf springs 154 and 156, the parallel linkmechanism 272 shown in FIG. 38 is located in such a manner that thehorizontal link portions 264 and 266 ride over the leaf springs 234 and236, and the distance between the horizontal link portions 264 and 266is increased.

With this arrangement, the movable member 82 may be more stablydisplaced in parallel to the displacement direction of the piezoelectricelement 72.

In the foregoing preferred embodiments shown in FIGS. 34 to 38, theconnecting member 104 may be removed when suitably setting an elasticforce of the hinge portions of the parallel link mechanism owing to theelasticity of the hinge portions. Thus, the quick return operation ofthe movable member 82 and the rolling member 92 may be ensured, and theparallel displacement of the movable member 82 in relation to thepiezoelectric element 72 may be also ensured.

Having thus described the preferred embodiments of the invention, itshould be understood that numerous structural modifications andadaptations may be made without departing from the spirit of theinvention.

What is claimed is:
 1. A device for magnifying displacement of apiezoelectric element adapted to be displaced by application of voltagethereto, comprising:a frame extending substantially parallel to adirection of displacement of said piezoelectric element, saidpiezoelectric element being mounted on said frame; a movable memberfixed to one end of said piezoelectric element with respect to saiddirection of displacement and adapted to be displaced in a directionsubstantially parallel to said frame; a first mount surface formed onsaid frame and extending substantially parallel to said direction ofdisplacement; a second mount surface formed on a surface of said movablemember which faces said first mount surface and extending substantiallyparallel to said direction of displacement, said second mount surfacefacing said first mount surface; a first leaf spring mounted at a firstend portion thereof on said first mount surface and extendingsubstantially parallel to said direction of displacement; a second leafspring mounted at a first end portion thereof on said second mountsurface and extending substantially parallel to said direction ofdisplacement, said second leaf spring being positioned adjacent to saidfirst leaf spring; and a rolling member fixed to second end portions ofsaid first and second leaf springs, wherein when said piezoelectricelement is displaced, said second leaf spring is displaced along saidfirst leaf spring through said movable member to roll said rollingmember.
 2. The device as defined in claim 1, wherein respective surfacesof said first and second leaf springs are in contact with each otherunder an inoperative condition of said piezoelectric element.
 3. Thedevice as defined in claim 1, wherein said first mount surface islocated at an end portion of an end surface of said frame, and saidsecond mount surface is located on an end surface of said movable memberoffset from a center line of said piezoelectric element to said frame.4. The device as defined in claim 3, wherein said frame has asubstantially L-shaped configuration as viewed from a side thereof suchthat said substantially L-shaped configuration is comprised of avertical portion extending substantially parallel to the direction ofdisplacement of said piezoelectric element and a base portion projectinglaterally from said vertical portion for supporting one end of saidpiezoelectric element with respect to the direction of displacement, andwherein said first leaf spring is fixed to an end surface of saidvertical portion of said frame, and said second leaf spring is fixed tothe end surface of said movable member opposed to said end surface ofsaid vertical portion.
 5. The device as defined in claim 1, wherein saidfirst and second leaf springs include respective deformable portionfacing each other, and said deformable portions are formed at theirfacing surfaces with respective noncontact portions for inhibitingcontact between said deformable portions.
 6. The devices as defined inclaim 5, wherein said deformable portions of said first and second leafsprings are formed with recesses on opposite surfaces to said facingsurfaces.
 7. The device as defined in claim 5, wherein said first andsecond leaf springs are formed from a single spring member in which asplit groove is formed which extends from a first end of said springmember toward a second end thereof, and said rolling member isintegrally connected to said second end.
 8. The device as defined inclaim 7, wherein said first leaf spring is fixed to an end surface ofsaid frame extending substantially parallel to said piezoelectricelement, and said second leaf spring is fixed to an end surface of saidmovable member opposed to said end surface of said frame and offset froma center line of said piezoelectric element to said frame.
 9. The deviceas defined in claim 7, wherein said split groove comprises a cutoutformed from said first end of said spring member toward said second endthereof.
 10. The device as defined in claim 7, wherein a head portion ofsaid spring member formed at said second end thereof without said splitgroove forms at least a part of said rolling member, thus integrallyforming the leaf springs with said at least a part of said rollingmember.
 11. The device as defined in claim 7, wherein said split groovecomprises a space defined by bending said spring member into a U-shapedconfiguration.
 12. The device as defined in claim 1, wherein said firstand second leaf springs are formed on their opposite surfaces withgrooves to form thin-walled portions opposed to each other at positionsof said grooves.
 13. The device as defined in claim 12, wherein saidgrooves are arranged at intervals in the direction of displacement ofsaid piezoelectric element.
 14. The device as defined in claim 1,wherein said first and second leaf springs have narrow portions eachhaving a width smaller than that of said fixed ends, respectively.
 15. Adevice for magnifying displacement of a piezoelectric element adapted tobe displaced .[.be.]. .Iadd.by .Iaddend.application of voltage thereto,comprising:a frame extending substantially parallel to a direction ofdisplacement of said piezoelectric element, said piezoelectric elementbeing mounted on said frame; a movable member fixed to one end of saidpiezoelectric element with respect to said direction of displacement; afirst mount .[.surfaced.]. .Iadd.surface .Iaddend.formed on said frameand extending substantially parallel to said direction of displacement;a second mount surface formed on a surface of said movable member andextending substantially parallel to said direction of displacement, andsecond mount surface facing said first mount surface; a first leafspring mounted at a first end portion thereof on said first mountsurface and extending substantially parallel to said direction ofdisplacement; a second leaf spring mounted at a first end portionthereof on said second mount surface and extending substantiallyparallel to said direction of displacement; a rolling member fixed tosecond end portions of said first and second leaf springs, wherein whensaid piezoelectric element is displaced, said second leaf spring isdisplaced along said first leaf spring through said movable member toroll said rolling member; and an elastically deformable connectingmember extending along said piezoelectric element on an opposite side ofsaid frame with respect to said movable member and connecting saidmovable member with a base portion of said frame, wherein when saidpiezoelectric element is displaced, said movable member is displacedsubstantially parallel to the direction of displacement against theelasticity of said connecting member to curve said second leaf springrelative to said first leaf spring and thereby roll said rolling member.16. The device as defined in claim 15, wherein said connecting member isformed independently of said frame and said movable member, and is fixedto said frame and said movable member.
 17. The device as defined inclaim 15, wherein said connecting member is formed by a plate-likemember having a width substantially parallel to a direction of thicknessof said leaf springs and having a small sectional area in a directionperpendicular to the width of said leaf spring.
 18. The device asdefined in claim 17, wherein a sectional area at end portions of saidconnecting member to be fixed to said movable member and said frame arelarger than a sectional area at an intermediate portion between saidfixed end portions.
 19. The device as defined in claim 15, wherein saidconnecting member normally applies a compression force to saidpiezoelectric element.
 20. A device for magnifying displacement of apiezoelectric element adapted to be displaced by application of voltagethereto, comprising:a frame extending substantially parallel to adirection of displacement of said piezoelectric element, saidpiezoelectric element being mounted on said frame; a movable memberfixed to one end of said piezoelectric element with respect to saiddirection of displacement; a first mount surface formed on said frameand extending substantially parallel to said direction of displacement;a second mount surface formed on a surface of said movable member andextending substantially parallel to said direction of displacement, saidsecond mount surface facing said first mount surface; a first leafspring mounted at a first end portion thereof on said first mountsurface and extending substantially parallel to said direction ofdisplacement; a second leaf spring mounted at a first end portionthereof on said second mount surface and extending substantiallyparallel to said direction of displacement; a rolling member fixed tosecond end portions of said first and second leaf springs, wherein whensaid piezoelectric element is displaced, said second leaf spring isdisplaced along said first leaf spring through said movable member toroll said rolling member; and a quadri-hinged parallel link mechanismprovided between said frame and said movable member for maintainingparallelism of said movable member to the direction of displacement ofsaid piezoelectric element.
 21. The device as defined in claim 20,wherein said quadri-hinged parallel link mechanism comprises a pair offirst and second link plates each comprising a pair of vertical parallellink portions fixed to a side surface of said frame and a side surfaceof said movable member, a pair of horizontal parallel link portionsextending between said vertical parallel link portions, and fourelastically deformable hinge portions connecting said vertical parallellink portions with said horizontal parallel link portions.
 22. Thedevice as defined in claim 21 further comprising a connecting portionfor connecting one of said vertical parallel link portions of said firstlink plate with .Iadd.an .Iaddend.opposite .[.on.]. one of said verticalparallel link portions of said second link plate.
 23. The device asdefined in claim 15 further comprising a quadri-hinged parallel linkmechanism provided between said frame and said movable member formaintaining parallelism of said movable member to the direction ofdisplacement of said piezoelectric element.
 24. The device as defined inclaim 1, wherein said rolling member comprises a base member fixed tosecond end positions of said first and second leaf springs; and an armconnected to said base member, said base member being formed with arecess for inserting a firm end of said arm.
 25. The device as definedin claim 1, wherein said rolling member is formed with a recess forinserting the second end portions of said first and second leaf springs.26. The device as defined in claim 10, wherein said rolling membercomprises said head portion and an arm connected to said head portion,said head portion being formed with a recess for inserting a first endof said arm.
 27. The device as defined in claim 12, wherein a spacingbetween said rolling member and said frame and between said rollingmember and said movable member is greater than a width of said grooves.28. The device as defined in claim 27, wherein said first leaf spring isfixed by brazing to said first mount surface of said frame, and saidsecond leaf spring is fixed by brazing to said second mount surface ofsaid movable member. .Iadd.29. A displacement magnifying devicecomprising:a frame; an elastic member having first and second connectionportions, said first connecting portion being secured to said frame; anelectro-distortion element having first and second opposite ends andresponsive to selective application of an electrical voltage thereto toundergo displacement, said first end being connected to said frame, saidsecond end being connected to said second connecting portion; and anelastically deformable restricting member for restricting displacementof said electro-distortion element, said elastically deformablerestricting member having first and second opposite restriction ends,said first restriction end being secured to a first connection partconnecting said frame to said first end of said electro-distortionelement, said second restriction end being secured to a secondconnection part connecting said second end of said electro-distortionelement to said second connecting portion of said elastic member..Iaddend. .Iadd.30. A displacement magnifying device comprising: aframe; a rolling member; an electro-distortion element having a firstend connected to said frame and responsive to selective application ofan electrical voltage thereto to undergo longitudinal expansion andcontraction; a first resilient member having a first end connected to asecond opposite end of said electro-distortion element and a second endconnected to said rolling member; a second resilient member disposed ina substantially parallel relationahip to said first resilient member andhaving a first end connected to said frame and a second end connected tosaid rolling member; and a restricting member, having first and secondportions, extending transversely to said first and second resilientmembers and fixedly connected at said first portion to saidelectro-distortion element and at said second portion to said frame,said restricting member restricting said electro-distortion element fromdisplacement away from said frame in a direction substantiallyperpendicular to said first and second resilient members. .Iaddend..Iadd.31. A printing head comprising a frame, a plurality of impactprinting wires constituting a wire-dot matrix and a plurality ofdisplacement magnifying devices respectively corresponding to, and forselectively driving, said respective impact printing wires, each of saiddisplacement magnifying devices comprising: a rolling member to whichthe respective one of said impact printing wires is connected; anelectro-distortion device having a first end connected to said frame andresponsive to selective application of an electrical voltage thereto toundergo longitudinal expansion and contraction; a first resilient memberhaving a first end connected to the second end of saidelectro-distortion device and thereby to said frame and a second endconnected to said rolling member; a second resilient member disposed insubstantially parallel relationship to said first resilient member andhaving a first end connected to said frame and a second end connected tosaid rolling member so that the extent of longitudinal expansion andcontraction of said electro-distortion device in response to theselective application of an electrical voltage thereto is enlarged bysaid rolling member and transmitted thereby to said impact printingwire; and a restricting member having first and second, opposite ends,extending transversely to said first and second resilient member andfixedly connected at the first end to said electro-distortion device andat the second, opposite end to said frame and thereby extendingtherebetween and restricting said electro-distortion device fromdisplacement away from said frame in a direction substantiallyperpendicular to said first and second resilient members. .Iaddend..Iadd.32. A printing head as set forth in claim 31, wherein said frameis substantially L-shaped having a base and a side wall extendingsubstantially perpendicular to said base, said electro-distortion devicehas one end connected to said base and the other end connected to saidresilient member, and said restricting member has one end connected tosaid side wall and the other end connected to said electro-distortiondevice in the vicinity of the other end thereof. .Iaddend. .Iadd.33. Aprinting head as set forth in claim 31, wherein said impact printingwire is connected to said rolling member at a first position thereof;said second end of said first reislient member is connected to saidrolling member at a second position thereof; and said second end of saidsecond resilient member is connected to said rolling member at a thirdposition thereof, said first and third positions being disposedoppositely, relatively to said second position, so that the extent oflongitudinal expansion and contraction of said electro-distortion deviceis enlarged by said rolling member and transmitted to said impactprinting wire. .Iaddend. .Iadd.34. A printing head as set forth in claim33, wherein a distance from said first position to said second positionis larger than a distance from said second position to said thirdposition. .Iaddend. .Iadd.35. A printing head comprising a frame, aplurality of impact printing wires constituting a wire-dot matrix and aplurality of displacement magnifying devices respectively correspondingto, and for selectively driving, said respective impact printing wires,each of said displacement magnifying devices comprising: a rollingmember to which the respective one of said impact printing wires isconnected; an electro-distortion device having a first end connected tosaid frame and responsive to selective application of an electricalvoltage thereto to undergo longitudinal expansion and contraction; afirst resilient member having a first end connected to the second end ofsaid electro-distortion device and thereby to said frame and a secondend connected to said rolling member; a second resilient member disposedin substantially parallel relationship to said first resilient memberand having a first end connected to said frame and a second endconnected to said rolling member so that the extent of longitudinalexpansion and contraction of said electro-distortion device in responseto the selective application of an electrical voltage thereto isenlarged by said rolling member and transmitted thereby to said impactprinting wire; and a restricting member connected between saidelectro-distortion device and said frame for restricting saidelectro-distortion device from displacement in a direction substantiallyperpendicular to said first and second resilient members. .Iaddend..Iadd.36. A device for magnifying displacement of an electro-distortionelement adapted to be displaced by application of voltage thereto,comprising: a frame extending substantially parallel to a direction ofdisplacement of said electro-distortion element, said electro-distortionelement being mounted on said frame; a movable member fixed to one endof said electro-distortion element with respect to said direction ofdisplacement; a first mount surface formed on said frame and extendingsubstantially parallel to said direction of displacement; a second mountsurface formed on a surface of said movable member and extendingsubstantially parallel to said direction of displacement, said secondmount surface facing said first mount surface; a first elastic member,mounted at a first end portion thereof on said first mount surface andextending substantially parallel to said direction of displacement; asecond elastic member mounted at a first end portion thereof on saidsecond mount surface and extending substantially parallel to saiddirection of displacement; a rolling member fixed to second end portionsof said first and second elastic members, wherein when saidelectro-distortion element is displaced, said second elastic member isdisplaced along said first elastic member through said movable member toroll said rolling member; and an elastically deformable connectingmember connected between said electro-distortion element and said frameto maintain said movable member substantially parallel with said framewhen said electro-distortion element is displaced, such that saidmovable member is displaced substantially parallel to the direction ofdisplacement against the elasticity of said connecting member to movesaid second elastic member relative to said first elastic member andthereby roll said rolling member. .Iaddend. .Iadd.37. The device asdefined in claim 36, wherein said connecting member is formedindependently of said frame and said movable member, and is fixed tosaid frame and said movable member. .Iaddend. .Iadd.38. The device asdefined in claim 36, wherein said connecting member is formed by anelongate member having a width substantially parallel to a direction ofthickness of said elastic members and having a small sectional area in adirection perpendicular to the width of said elastic members. .Iaddend..Iadd.39. The device as defined in claim 38, wherein a sectional area atend portions of said connecting member to be fixed to said movablemember and said frame are larger than a sectional area at anintermediate portion between said fixed end portions. .Iaddend..Iadd.40. The device as defined in claim 36, wherein said connectingmember normally applies a compression force to said electro-distortionelement. .Iaddend. .Iadd.41. A device as defined in claim 36, whereinsaid first and second elastic members are leaf springs. .Iaddend..Iadd.42. A device as defined in claim 36, wherein said connectingmember extends substantially parallel to said first and second elasticmembers. .Iaddend. .Iadd.43. A device as defined in claim 36, whereinsaid connecting member extends substantially perpendicular to said firstand second elastic members. .Iaddend. .Iadd.44. A device for magnifyingdisplacement of an electro-distortion element adapted to be displaced byapplication of voltage thereto, comprising: a frame extendingsubstantially parallel to a direction of displacement of saidelectro-distortion element, said electro-distortion element beingmounted on said frame; a movable member fixed to one end of saidelectro-distortion element with respect to said direction ofdisplacement; a first mount surface formed on said frame and extendingsubstantially parallel to said direction of displacement; a second mountsurface formed on a surface of said movable member and extendingsubstantially parallel to said direction of displacement, said secondmount surface facing said first mount surface; a first elastic membermounted at a first end portion thereof on said first mount surface andextending substantially parallel to said direction of displacement; asecond elastic member mounted at a first end portion thereof on saidsecond mount surface and extending substantially parallel to saiddirection of displacement; a rolling member fixed to second end portionsof said first and second elastic members, wherein when saidelectro-distortion element is displaced, said second elastic member isdisplaced along said first elastic member through said movable member toroll said rolling member; and an elastically deformable mechanismprovided between said frame and said movable member for maintainingparallelism of said movable member to the direction of displacement ofsaid electro-distortion element. .Iaddend. .Iadd.45. A device as definedin claim 44, wherein said first and second elastic members are leafsprings. .Iaddend. .Iadd.46. A device as defined in claim 44, whereinsaid deformable mechanism is an elongate member extending substantiallyparallel to said first and second elastic members. .Iaddend. .Iadd.47. Adevice as defined in claim 44, wherein said deformable mechanism is aquadri-hinged parallel link. .Iaddend. .Iadd.48. The device as definedin claim 47, wherein said quadri-hinged parallel link comprises a pairof first and second link plates each comprising a pair of verticalparallel link portions fixed to a side surface of said frame and a sidesurface of said movable member, a pair of horizontal parallel linkportions extending between said vertical parallel link portions, andfour elastic deformable hinge portions connecting said verticallyparallel link portions with said horizontal parallel link portions..Iaddend. .Iadd.49. The device as defined in claim 48, furthercomprising a connecting portion for connecting one of said verticalparallel link portions of said first link plate with an opposite one ofsaid vertical parallel link portions of said second link plate..Iaddend.